1. Field of the Invention
The invention relates to a sheathed-element glow plug which includes a glow plug body, a heating rod arranged therein, a heating element and, optionally, a control element associated with said heating element.
2. Description of the Related Art
In multi-polar glow plugs, in particular those plugs in which an ionic current measurement is carried out via the surface of the heating rods, the heating rods must be installed so that they are insulated from the glow plug body. In this situation, glow plugs are known where the glow plug body comprises two separate components, where one component is arranged coaxially in the other and with the components being fixed so as to be electrically insulated from each other by a glass seal formed by melting. With this arrangement, the inner component is used as the outside pole of the heating rod.
However, from a technical point of view it is nearly impossible to fabricate such a structure for smaller glow plugs, and, therefore, production of such smaller glow plugs cannot be undertaken using the normal production methods and devices.
It is therefore an object of the invention to avoid the disadvantages known in the construction of smaller glow plugs of prior art by providing an improved glow plug construction and a method of producing generic sheathed-element glow plugs of the type described above that can be fabricated using conventional production apparatus for sheathed-element glow plugs. Furthermore, it is an object of the invention to provide smaller glow plugs of a safe contact arrangement, for example, by means of coaxial connectors while at the same time ensuring good mechanical stability of the smaller glow plugs and the contact connections.